The maintenance and monitoring of fluids in vehicles, engines, pumps, weapons and machinery (all hereinafter, for convenience, generically referred to as “vehicles”) is vital to ensuring reliable operation. While there is no single sensor available that can monitor all fluids simultaneously, due to the wide variation in composition and fluid failure mechanisms, a suite of networked, miniaturized onboard vehicle fluid sensors can be envisioned for continuous, in-situ monitoring of fluid degradation. In the case of brake fluid and hydraulic fluid, the main mechanism for fluid degradation is humidity absorption, excess particulates (metal and sand), and solvent contamination. In-line hydraulic fluid humidity sensors are commercially available from several sources. In the case of engine coolant, increased acidity leads to corrosion in internal engine components. The pH monitoring of coolant is beneficial, and could be implemented using commercial sensors (e.g. Durafet III pH electrode from Honeywell), which could be packaged for use in vehicles by a third party. In the case of engine oil, there are dielectric [1,2], viscosity, conductivity [3], chromatic modulation [4], x-ray fluorescence, infrared and other sensors used to detect changes in the observable fluid properties [5]. Several sensor systems are available which examine changes in dielectric permittivity and viscosity of oil [22], as are vehicle-specific software systems that predict oil failure based on past driving conditions (deployed by General Motors) [6]. There are to date, however, no commercially-available sensors that provide a rigorous, real-time detection of the most fundamental chemical mechanism of engine lubricating oil failure, —the formation of free radicals by the breakdown of long hydrocarbon molecular chains in oil. Only the overall results stemming from these free radical-induced changes have heretofore been monitored in-situ, but not the direct detection of the free radicals themselves.
Onboard monitoring of lubricant engine oil degradation provides a reduction in engine wear and reduced maintenance costs for the end-user [6]. The net economic benefit of this optimized maintenance schedule can be very large. In the United States, over one billion gallons of motor oil are used each year; thus any reduction in oil usage can have a significant impact. In civilian automotive applications, engine oil is typically changed every 3000-7500 miles, while coolant, brake fluid and automatic transmission fluid are changed every 30 k-50 k miles. The economic benefit to the end user of optimized engine oil management may be greater than for other automotive fluids, both in reduced fluid costs and in reduced wear of engine components.
Using flexural mechanical structures similar to earlier U.S. Pat. Nos. 5,964,242, 6,914,785 and 7,025,324, the present invention proposes to optimize a miniature electron spin resonance (ESR) sensor for the detection particularly, though not exclusively, of molecular peroxy radicals in engine oil and related or other fluids. The breakdown of engine oil is indicated by a sharp increase in the concentration of damaging peroxy radicals (RO2·) among others in the oil. Peroxy radicals are readily identified by electron spin resonance (ESR) spectroscopy and thus give a clear and direct indication of the engine oil condition.
Numerous systems have before been developed by auto manufacturers and others for improved automotive fluids management. Researchers have prototyped the use of viscosity sensors, dielectric sensors, chromatic sensors (sensing color changes), oil pH sensors, miniature fourier transform infrared spectrometers (FTIR) and x-ray fluorescence sensors, sensors of magnetic particles are of iron-derived and transition metal particles and combinations thereof. General Motors employs a computer model, which uses the car driving history, environmental conditions (temperature, humidity) and maintenance history to predict when the oil must be changed, without specialized sensors, although detailed data from millions of miles of road tests was required to create this computer model [6]. The present invention, however, differs from these approaches in a fundamental way: directly in situ sensing the molecular changes that occur in oil as a result of breakdown of the lubricant.